Olefin compounds can be categorized into vinyls, vinylidenes, 1,2-di-substituted olefins and tri-substituted olefins depending on the substitution on the two carbon atoms connected by an ethylenic C═C bond. A vinyl olefin, represented by RCH═CH2, contains one substituent R and three hydrogen atoms; a vinylidene, represented by C(R1R2)═CH2, contains two substituents (R1 and R2) connected to the same carbon atom and two hydrogen atoms connected to the other carbon atom. A 1,2-di-substituted vinylene, represented by CH(R1)═CH(R2), contains two substituents (R1, R2) with one connected to each carbon atom. A tri-substituted vinylene, represented by CH(R1)═C(R2R3), contains three substituents (R1, R2, R3) with only one hydrogen atom left. Vinyls and vinylidenes are terminal olefins, while 1,2-di-substituted vinylenes and tri-substituted vinylenes are internal olefins. Among these four types of olefins, vinylidenes are particularly desirable due to its reactivity and are frequently used to make derivatives of the olefin for use in various applications.
Oligomeric, ethylenically unsaturated molecules made from the polymerization of terminal olefins are known. For example, U.S. Pat. No. 8,748,361 B2 discloses a mixture comprising unsaturated polyalpha-olefin (“uPAO”) material made from, e.g., oligomerization of terminal olefins in the presence of metallocene catalysts. It was disclosed in this reference that the uPAOs could comprise, among others, vinyls, vinylenes, 1,2-di-substituted vinylenes, and tri-substituted vinylenes.
Recently, however, research and development in various chemical fields reveal that the ethylenically unsaturated PAO materials prepared from oligomerization of linear terminal olefins can be particularly advantageously used as intermediates for making various specialty chemicals because of the reactivity of the C═C double bond present in molecular structure of the oligomer molecules. For example, various chemical functional groups can be bonded to the carbon backbone of the uPAO molecule when a chemical agent reactive with the C═C bond is allowed to contact the uPAO material. The functional group thus introduced onto the PAO structure can bring about unique properties to the functionalized and saturated PAO molecules.
It has been found that the reactivity of the C═C bonds in vinyls, vinylidenes, 1,2-di-substituted vinylenes and tri-substituted vinylenes are different with regard to many chemical functionalization agents. For a specific type of functionalization agent, one or more particular type(s) of olefin(s) may be more desirable than the other(s). In addition, uPAOs having various molecular weight and molecular weight distribution and differing reactivities may be desired for making differing derivatives comprising differing functional groups thereon. For example, dimers of olefins as specific uPAOs can be of higher interest and value over higher oligomers such as trimers and tetramers. Furthermore, it is known that vinylidenes and tri-substituted vinylenes are more reactive than 1,2-di-substituted vinylenes with many common reagents reactive with C═C double bonds. Thus, high-purity vinylidene dimers of terminal olefins and methods for making them are of high interest.
U.S. Pat. No. 4,658,078 discloses a process for making vinylidene dimers from 1-olefins such as propylene, 1-hexene, and 1-octene by using a catalyst system comprising bisCpZrCl2 and methylalumoxane. While impressive selectivity of the terminal olefin toward dimers was achieved in the examples of this patent, the oligomerization step nonetheless resulted in the formation of high quantity of trimers and higher oligomers, rendering the oligomer products from the oligomerization reaction step not directly useable as a high-purity vinylidene dimer. One would need to distill the oligomer products in order to reduce the trimers and higher oligomers to an acceptable level. Moreover, the process illustrated in this patent was a batch process, which is not efficient in producing large quantities of vinylidene dimer products. In addition, there is no teaching in this patent, particularly in the examples, of the selectivity of the 1-olefin monomers toward vinylidenes in the dimer product.
Thus, there remains a need for a process for making vinylidene olefins from terminal olefins. This disclosure satisfies this and other needs.